Precise measurements are the key to advances in all fields of science. Quantum entanglement shows higher sensitivity than achievable by classical methods. Most physical quantities including position, displacement, distance, angle, and optical path length can be obtained by optical phase measurements. Reducing the photon wavelength of the interferometry can further enhance the optical path length sensitivity and imaging resolution. By quantum frequency up conversion, we realized a short wavelength two photon number entangled state. Nearly perfect Hong Ou Mandel interference is achieved after both 1547-nm photons are up converted to 525 nm. Optical phase measurement of two photon entanglement state yields a visibility greater than the threshold to surpass the standard quantum limit. These results offer new ways for high precision quantum metrology using short wavelength quantum entanglement number state.
@article{arxiv.1703.04253,
title = {Super-resolving phase measurement with short wavelength NOON states by quantum frequency up-conversion},
author = {Zhi-Yuan Zhou and Shi-Long Liu and Shi-Kai Liu and Yin-Hai Li and Dong-Sheng Ding and Guang-Can Guo and Bao-Sen Shi},
journal= {arXiv preprint arXiv:1703.04253},
year = {2017}
}